FIELD OF THE INVENTION
The invention relates to a cooling system having a cooling pipe for cooling a containment chamber that serves to receive core melt of a reactor core of a nuclear power plant.
In order to provide safe operation, nuclear power plants have numerous diverse and redundant safety systems, including cooling systems, through the use of which operating conditions that deviate from normal operating conditions can be detected early and counteracted. As a result, such safety-critical states as reactor core meltdown are practically precluded.
In order to control that kind of accident, which is considered hypothetical, German Published, Non-Prosecuted Patent Application DE 40 41 295 A1, corresponding to U.S. Pat. No. 5,343,506, describes a core retainer and a method for emergency cooling of a nuclear power plant. The core retainer has a catch basin, which is disposed immediately below the reactor pressure vessel that encloses the reactor core. Both the catch basin and the reactor pressure vessel are disposed inside a reactor cavern, which is a concrete structure. Cooling channels extend along the floor and the walls of the catch basin between the catch basin and the concrete structure and coolant water can be carried through the cooling channels. The cooling channels on the floor communicate with a water supply and discharge into a cooling pipe that protrudes in siphonlike fashion into the water supply. The siphonlike cooling pipe includes one part shaped as an inverted U. The apex of the U is located above an operative level of the water supply, and although the cooling pipe does dip into the water supply, in the vicinity of its apex it protrudes out of the water supply. As a result, as long as the level is at the operative level, no coolant water enters the cooling channels. It is not until the water supply is flooded to a level higher than the apex of the U that coolant water enters the cooling channels, resulting in cooling of the outside of the catch basin. Cooling of the interior of the catch basin is carried out through a flood pipe, which is passed from the water supply through the concrete structure into the catch basin. The flood pipe is closed in the catch basin by a meltable stopper that does not melt open until at a high ambient temperature, thus allowing coolant water to flow into the interior of the catch basin. Coolant water is present in the flood pipe even during normal operation of the nuclear power plant, and as a result the meltable stopper is continuously cooled.